Insert-molded, externally manifolded, sealed membrane based electrochemical cell stacks

ABSTRACT

The present invention provides, among other things, membrane cassettes and stacks thereof which are suitable for a use in a variety of electrochemical applications. The invention further provides membrane cassettes which comprise one or more external manifolds which deliver reagents and/or coolant to one or more reactant or coolant flow fields of the membrane cassettes. In particular, the present invention describes the insert molding method, whereby the plenums of the external manifolds are created during the stack encapsulation step. The invention describes several methods for creating the manifold runner geometry via insert-molding, machining, or with separate components.

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/401,785, filed Apr. 10, 2006, which application isincorporated in its entirety by reference.

BACKGROUND OF THE INVENTION

Membrane based electrochemical cells, and particularly, proton exchangemembrane (PEM) fuel cells are well known. PEM fuel cells convertchemical energy to electrical power with virtually no environmentalemissions and differ from a battery in that energy is not stored, butderived from supplied fuel. Therefore, a fuel cell is not tied to acharge/discharge cycle and can maintain a specific power output as longas fuel is continuously supplied. Significant funds have been investedin fuel cell research and commercialization, indicating that thetechnology has considerable potential in the marketplace. However, thehigh cost of fuel cells when compared to conventional power generationtechnology deters their widespread use. The cost of fabricating andassembling fuel cells can be significant due to the materials and laborinvolved. Indeed, as much as 85% of a fuel cell's cost can be attributedto manufacturing.

Traditionally, one of the problems of using internally manifolded stacksin fuel cells and other electrochemical applications, is the area thatis sacrificed in sealing around the internal manifolds. One remedy is tolocate some or all of the manifolds external to the stack. Onedifficulty associated with that design is experienced in sealing betweenthe manifold and the stack. As in traditional stacks, sealing istypically accomplished with gaskets and compression. Unfortunately,gasket/compression based seals have a number of inherent drawbacks,including a sensitivity to thermal cycling, requirements of uniformcompression and associated hardware, high tolerance parts, and delicateassembly requirements.

In general, a single cell PEM fuel cell consists of an anode and acathode compartment separated by a thin, ionically conducting membrane.This catalyzed membrane, with or without gas diffusion layers, is oftenreferred to as a membrane electrode assembly (MEA). Energy conversionbegins when the reactants, reductants and oxidants, are supplied to theanode and cathode compartments, respectively, of the PEM fuel cell.Oxidants include pure oxygen, oxygen-containing gases, such as air, andhalogens, such as chlorine. Reductants, also referred to herein as fuel,include hydrogen, natural gas, methane, ethane, propane, butane,formaldehyde, methanol, ethanol, alcohol blends and other hydrogen richorganics. At the anode, the reductant is oxidized to produce protons,which migrate across the membrane to the cathode. At the cathode, theprotons react with the oxidant. The overall electrochemical redox(reduction/oxidation) reaction is spontaneous, and energy is released.Throughout this reaction, the PEM serves to prevent the reductant andoxidant from mixing and to allow ionic transport to occur.

Current state of the art fuel cell designs comprise more than a singlecell, and in fact, generally combine several MEAs, flow fields andseparator plates in a series to form a fuel cell “stack”; therebyproviding higher voltages and the significant power outputs needed formost commercial applications. Flow fields allow for the distribution ofthe reactants through the fuel cell and are typically separate from theporous electrode layers within the fuel cell. Depending on stackconfiguration, one or more separator plates may be utilized as part ofthe stack design to prevent mixing of the fuel, oxidant and coolingstreams within the fuel cell stack. Such separator plates can alsoprovide structural support to the stack.

Bipolar plates perform the same function as an oxidant flow field, fuelflow field and separator plate in combination and are often used in thedesign of fuel cells as their use can reduce the number of componentsrequired in the functioning fuel cell. These bipolar plates contain anarray of channels formed in the surface of the plate contacting an MEAwhich function as the flow fields. The lands conduct current from theelectrodes while the channels between the lands serve to distribute thereactants utilized by the fuel cell and facilitate removal of reactionby-products, such as water. Fuel is distributed from the fuel inlet portto the fuel outlet port, as directed by the channels, on one face of thebipolar plate, while oxidant is distributed from the oxidant inlet portto the oxidant outlet port, as directed by the channels, on the opposingface of the bipolar plate, and the two faces are not connected throughthe plate. The particular design of the bipolar plate flow fieldchannels may be optimized for the operational parameters of the fuelcell stack, such as temperature, power output, gas humidification andflow rate. Ideal bipolar plates for use in fuel cell stacks are thin,lightweight, durable, highly conductive, corrosion resistant structuressuch as carbon/polymer composites or graphite. In the fuel cell stack,each bipolar plate serves to distribute fuel to one MEA of the stackthrough its fuel flow field face while distributing oxidant to a secondMEA through the opposite oxidant flow field face. A thin sheet of porouspaper, cloth or felt, usually made from graphite or carbon, may bepositioned between each of the flow fields and the catalyzed faces ofthe MEA to support the MEA where it confronts grooves in the flow fieldto conduct current to the adjacent lands, and to aid in distributingreactants to the MEA. This thin sheet is normally termed a gas diffusionlayer (GDL) and can be incorporated as part of the MEA.

Of necessity, certain stack components, such as the GDL portion of theMEA, are porous in order to provide for the distribution of reactantsand byproducts into, out of, and within the fuel cell stack. Due to theporosity of elements within the stack, a means to prevent leakage of anyliquid or gases between stack components (or outside of the stack) aswell as to prevent drying out of the various stack elements due toexposure to the environment is also needed. To this end, gaskets orother seals are usually provided between the surfaces of the MEA or PEMand other stack components and on portions of the stack periphery. Thesesealing means, whether composed of elastomeric or adhesive materials,are generally placed upon, fitted, formed or directly applied to theparticular surfaces being sealed. These processes are labor intensiveand not conducive to high volume manufacturing, thereby adding to thehigh cost of fuel cells. Additionally, the variability of theseprocesses results in poor manufacturing yield and poor devicereliability.

Fuel cell stacks may also contain humidification channels within one ormore of the coolant flow fields. These humidification channels provide amechanism to humidify fuel and oxidants at a temperature as close aspossible to the operating temperature of the fuel cell. This helps toprevent dehydration of the PEM as a high temperature differentialbetween the gases entering the fuel cell and the temperature of the PEMcauses water vapor to be transferred from the PEM to the fuel andoxidant streams.

Fuel cell stacks range in design depending upon power output, cooling,and other technical requirements, but may utilize a multitude of MEAs,seals, flow fields and separator plates, in intricate assemblies thatresult in manufacturing difficulties and further increased fuel cellcosts. These multitudes of individual components are typically assembledinto one sole complex unit. The fuel cell stack is formed by compressingthe unit, generally through the use of end plates and bolts althoughbanding or other methods may be used, such that the gaskets seal and thestack components are held tightly together to maintain electricalcontact there between. These conventional means of applying compressionadd even more components and complexity to the stack and pose additionalsealing requirements.

Various attempts have been made in the fuel cell art to address thesedeficiencies in fuel cell stack assembly design and thereby lowermanufacturing costs. However, most stack assembly designs still requiremanual alignment of the components, active placement of the sealingmeans and/or a multi-step process, each of which presents notabledisadvantages in practice. See, e.g., the processes described in U.S.Pat. No. 6,080,503, to Schmid et al., U.S. Pat. No. 4,397,917, to Chi etal., and U.S. Pat. No. 5,176,966, to Epp et al.

Additionally, in traditional fuel cell cassettes, two types of MEAsdominate; MEAs in which 1) the membrane extends beyond the borders ofthe gas diffusion layers, and 2) gasket materials are formed into theedges of the MEA itself with the membrane and GDLs approximately of thesame size and shape (see, e.g., U.S. Pat. No. 6,423,439 to Ballard). Inthe first type, separate gaskets are used to seal between the membraneedge extending beyond the GDL and the other part of the stack (bipolarplates). In the second type, the gasket of the MEA seals directly to theother parts of the stack. Each of these methods requires compression tomake a seal. These compressive-based seals require that all thecomponents in the stack have high precision such that a uniform load ismaintained. MEA suppliers have become accustomed to supplying the MEAformats above.

Still other attempts have been made to improve upon fuel cell design andperformance. For instance, U.S. Pat. No. 4,212,929 describes an improvedsealing method for fuel cell stacks. That patent reports a sealingsystem which utilizes a polymer seal frame clamped between the manifoldand the stack. As described, the seal frame moves with the stack and theleak rate associated with a typical manifold seal is reduced duringcompression. U.S. Pat. No. 5,514,487 and U.S. Pat. No. 5,750,281 bothdescribe an edge manifold assembly which comprises a number of manifoldplates. The plates are mounted on opposite sides of the fuel cell stackand function in such a way to selectively direct the reactant andcoolant streams along the perimeter of the stack. While these designsoffer limited improvements to other conventional assemblies, they aregenerally unsuitable for high-volume manufacture.

Recognizing these and other deficiencies in the art, the Assignee ofthis application has developed a series of innovative methods forsealing manifold ports within the stack or a module thereof, as well asmethods for sealing the stack or module periphery that are less laborintensive and more suitable to high-volume manufacturing processes (seeWorld Publication WO 03/036747). That publication discloses a ‘one-shot’assembly of fuel cell stacks (and other electrochemical devices) inwhich all of the component parts are assembled into a mold withoutgaskets. A resin is introduced into the mold and this resin selectivelypenetrates certain portions of the assembly either by resin transfermolding or injection molding techniques. Upon hardening, that resinseals the components and defines all the manifold channels within thestack. The net effect is to replace the gaskets of the traditional stackwith adhesive based seals, introduced after the assembly of thecomponents.

We also have previously described fuel cells having an MEA in which theGDL and membrane were more or less of the same general outline as eachother and of the overall stack profile (see World Publication WO03/092096). The major advantage of this technique is the ability todirectly use a roll-to-roll MEA without having to do any postprocessing. However, a substantial portion of the cross-section of eachMEA is used for sealing the various manifold openings and periphery ofthe stack such that only about 50% of the cell cross section is used forthe electrochemical reaction.

We also have developed membrane-based electrochemical cells, and moreparticularly, PEM fuel cell stacks which comprise one or more compositeMEAs having a molded gasket about the periphery. The gasket portion ofthe composite MEA has one or more features capable of regulating theflow of sealant during sealing processes (see World Publication2004/047210).

In another previous patent application, the Assignee of this applicationreported on an innovative fuel cell stack design which assemblestogether individual modules to form a fuel cell stack of requisite poweroutput where each module permanently binds a number of unit cellstogether (see World Publication WO 02/43173, incorporated herein byreference).

Despite these advancements over the prior the art, the Assignee of thisapplication has recognized that further improvements can be made to thetechnology. One improvement, for example, would be to utilize a moresignificant portion of the total MEA area for the electrochemicalprocess. For instance, with particular reference to those fuel cellstacks which include an internal manifold design, a certaincross-section of the cassette must be utilized for sealant channels andreactant/coolant manifolds; thus, that potentially active area isnecessarily sacrificed. It also would be desirable to provide animproved fuel cell stack design that is less complex, more reliable, andless costly to manufacture. Additionally, it would be highly desirableto provide improved fuel cell stacks having reduced weight and size and(as noted above) in which a greater percent of the total MEA surfacearea is available for use in the electrochemical reaction occurringwithin the stack, e.g., available for catalyst area and proton transfer.

It also would be particularly desirable to develop stacks with featuresthat reduce or eliminate coolant permeation, cross-leaks and externalleaks, and which provide for uniform mating of internal components, suchas the bipolar and cooling plates.

It would also be highly desirable to develop alternate embodiments. Twosuch examples include an insert molded method using separaterunner/bridge components (wherein these components would eliminate theneed for a hole in the side of the bi-polar plates), and second is amethod utilizing alternate shapes for the plenum inserts (to optimizeassembly and/or fuel cell performance).

SUMMARY OF THE INVENTION

The purpose and advantages of the present invention will be set forth inand apparent from the description that follows, as well as will belearned by practice of the invention. Additional advantages of theinvention will be realized and attained by the methods and systemsparticularly pointed out in the written description and claims hereof,as well as from the appended drawings. To achieve these and otheradvantages and in accordance with the purpose of the invention, asembodied herein and broadly described, the invention includes a fuelcell stack having at least one fuel cell with a membrane electrodeassembly, a reductant flow field disposed proximate a first side of themembrane electrode assembly, the reductant flow field including areductant flow channel extending to a periphery of the fuel cell, and anoxidant flow field disposed proximate a first side of the membraneelectrode assembly, the oxidant flow field including an oxidant flowchannel extending to the periphery of the fuel cell.

The fuel cell stack also includes a unitary plenum housing formed aboutthe periphery of the fuel cell, the unitary plenum housing at leastpartially defining a reductant manifold in fluid communication with thereductant flow channel, the reductant manifold and the reductant flowchannel cooperating to form a reductant plenum, and an oxidant manifoldin fluid communication with the oxidant flow channel, the oxidantmanifold and the oxidant flow channel cooperating to form an oxidantplenum.

In accordance with a further aspect of the invention, the fuel cell canfurther include a coolant plate in thermal communication with themembrane electrode assembly, the coolant plate including a coolant flowchannel extending to the periphery of the fuel cell, and the unitaryplenum housing can further define a coolant manifold in fluidcommunication with the coolant flow channel, the coolant manifold andthe coolant flow channel cooperating to form a coolant plenum.

The cell stack can further include a vapor barrier insert disposedproximate at least one of the oxidant, reductant and coolant manifolds,the vapor barrier insert being adapted and configured to reduce egressof fluids through a periphery of the fuel cell stack. The vapor barrierinsert can be surrounded by molded material of the plenum housing. Thefuel cell stack can further include a vapor barrier layer disposedproximate the external periphery of the plenum housing, the vaporbarrier layer being adapted and configured to reduce egress of fluidsthrough a periphery of the fuel cell stack. The vapor barrier insert canbe made from a material selected from among plastic, metal, compositematerial, any other suitable material, and combinations thereof.

In accordance with another aspect of the invention, the unitary plenumhousing can define the reductant manifold in cooperation with a portionof the periphery of the fuel cell. The portion of the periphery of thefuel cell includes at least one of an edge of the membrane electrodeassembly and an edge of a plate.

In accordance with still another aspect of the invention, the unitaryplenum housing can define the oxidant manifold in cooperation with aportion of the periphery of the fuel cell. The portion of the peripheryof the fuel cell can include at least one of an edge of the membraneelectrode assembly and an edge of a plate.

In accordance with a further aspect of the invention, the unitary plenumhousing can define the coolant manifold in cooperation with a portion ofthe periphery of the fuel cell. The portion of the periphery of the fuelcell includes at least one of an edge of the membrane electrode assemblyand an edge of a plate.

In accordance with another aspect of the invention, it is possible forthe reductant manifold to not be defined by the periphery of the fuelcell. It is possible for the oxidant manifold to not be defined by theperiphery of the fuel cell. Moreover, it is also contemplated that it ispossible for the coolant manifold to not be defined by the periphery ofthe fuel cell.

In accordance with still another aspect of the invention, the fuel cellstack can include a plurality of fuel cells electrically connected inseries. The fuel cell stack can also include a plurality of coolingplates in thermal communication with the fuel cells.

In accordance with a further aspect of the invention, the reductant flowfield and oxidant flow field can each be integrally formed into aseparator plate, the separator plate being chosen from the groupincluding a bipolar plate and a cooling plate. The reductant flowchannel and the oxidant flow channel can each terminate at the peripheryof the fuel cell at a port that extends only partially through thethickness of the separator plate.

Each separator plate can define a contoured feature proximate a port ofa flow channel at the periphery of the fuel cell, the contoured featurebeing adapted and configured to mate with a removable mold when theplenum housing is being formed. The contoured feature can besubstantially concave in shape and can be adapted to receive a mold thatis substantially cylindrical in shape when the plenum housing is beingformed. The separator end plate can include material selected from amongcarbon/polymer composite material, graphite, metal, and any othersuitable material. It is also contemplated that graphite can includegraphite tape. The bipolar plate can be stamped from a metal sheet.

In accordance with another aspect of the invention, the reductant flowfield includes a second reductant flow channel extending to a peripheryof the fuel cell and the oxidant flow field includes a second oxidantflow channel extending to the periphery of the fuel cell. The unitaryplenum housing can further define a second reductant manifold in fluidcommunication with the second reductant flow channel, the secondreductant manifold and the second reductant flow channel cooperating toform a second reductant plenum, and a second oxidant manifold in fluidcommunication with the second oxidant flow channel, the second oxidantmanifold and the second oxidant flow channel cooperating to form asecond oxidant plenum.

In accordance with still another aspect of the invention, the coolantplate can include a second flow channel extending to the periphery ofthe fuel cell, and the unitary plenum housing can further define asecond coolant manifold in fluid communication with the second coolantflow channel, the second coolant manifold and the second coolant flowchannel cooperating to form a second coolant plenum.

In accordance with a further aspect of the invention, the active area ofthe membrane electrode assembly can be maximized by not providing anaperture passing through the fuel cell along a direction from a firstendplate of the stack toward a second end plate of the stack.

In accordance with still another aspect of the invention, the fuel cellstack can further include a first end plate at a first end of the stackand a second end plate at the second end of the stack. The fuel cellstack can further include a plurality of fasteners for connecting thefirst and second end plates to each other to hold the fuel cell inplace. At least one of the end plates can include recesses formedtherein proximate an extremity of one of the manifolds, the recess beingadapted and configured to receive a removable mold when the plenumhousing is being formed.

It is also contemplated that each end plate can include materialselected from among a thermoset polymer, a thermoplastic polymer, ametal, a metal alloy, a filled polymer composite material, any othersuitable material, and combinations thereof. In accordance with stillanother aspect of the invention, one of the endplates can include a fillhole and the other end plate can include a vent hole to facilitateforming the plenum housing by way of a molding process.

In accordance with a further aspect of the invention, the fuel cellstack can further include an electrical current collector electricallycoupled to the membrane electrode assembly. It is also contemplated thatat least one of the end plates can include ports in fluid communicationwith the reductant plenum and oxidant plenum for transporting materialsthrough the fuel cell stack.

In accordance with another aspect of the invention, at least one of themanifolds can have a tapered configuration from a first end of themanifold to a second end of the manifold. The tapered manifold can havea smaller transverse dimension that enlarges to a larger transversedimension along a length of the manifold toward an external port of thefuel cell stack. The tapered manifold can be defined by a substantiallycylindrical surface proximate the periphery of the fuel cell, and atapering surface opposite the substantially cylindrical surface.

In accordance with still another aspect of the invention, the fuel cellstack can further include a tubular insert integrally formed into oneend of one of the manifolds, the tubular insert made from a materialthat is compatible with the material of the plenum housing, wherein thetubular insert forms a portion of a fluid flow path including themanifold to which it is attached. The tubular insert can protrudethrough a port of an end plate of the fuel cell stack proximate theplenum housing.

The invention also includes a method for manufacturing a fuel cellstack. The method includes providing at least one fuel cell having amembrane electrode assembly, a reductant flow field disposed proximate afirst side of the membrane electrode assembly, the reductant flow fieldincluding a reductant flow channel extending to a periphery of the fuelcell, and an oxidant flow field disposed proximate a first side of themembrane electrode assembly, the oxidant flow field including an oxidantflow channel extending to the periphery of the fuel cell. The methodalso includes molding a plenum housing about the periphery of the fuelcell, the plenum housing at least partially defining a reductantmanifold in fluid communication with the reductant flow channel, thereductant manifold and the reductant flow channel cooperating to form areductant plenum, and an oxidant manifold in fluid communication withthe oxidant flow channel, the oxidant manifold and the oxidant flowchannel cooperating to form an oxidant plenum.

In further accordance with the invention, the fuel cell can furtherinclude a coolant plate in thermal communication with the membraneelectrode assembly, the coolant plate including a coolant flow channelextending to the periphery of the fuel cell and the molding step caninclude forming can include forming a coolant manifold in fluidcommunication with the coolant flow channel, the coolant manifold andthe coolant flow channel cooperating to form a coolant plenum.

The molding step can define an interior surface of at least one of theoxidant manifold, reductant manifold and coolant manifold in cooperationwith a portion of the periphery of the fuel cell. The portion of theperiphery of the fuel cell includes at least one of an edge of membraneelectrode assembly and an edge of a plate. It is possible for at leastone of the oxidant manifold, reductant manifold, and coolant manifold tonot be defined by the periphery of the fuel cell.

The coolant plate can include a second coolant flow channel extending tothe periphery of the fuel cell and the molding step can further includeforming a second coolant manifold in fluid communication with the secondcoolant flow channel, the second coolant manifold and the second coolantflow channel cooperating to form a second coolant plenum.

The method can further include positioning a vapor barrier insertproximate at least one of the oxidant, the reductant and coolantmanifolds prior to the molding step, the vapor barrier insert beingadapted and configured to reduce egress of fluids through a periphery ofthe fuel cell stack once molded in place. The vapor barrier insert canbe made from a material selected from plastic, metal composite material,any other suitable material, and combinations thereof.

In accordance with another aspect of the invention, the method canfurther include integrally forming the reductant flow field and oxidantflow field into a separator plate, the separator plate being chosen fromthe group consisting of a bipolar plate and a cooling plate. The methodcan further include forming a contoured surface in the edge of eachseparator plate proximate a port of a flow channel at the periphery ofthe fuel cell, the contoured surface being adapted and configured tomate with a removable manifold mold.

The contoured feature can be substantially concave in shape and can beadapted to receive a mold that is substantially cylindrical in shapewhen the plenum housing is being formed. The method can further includeforming a recess in an end plate of the fuel cell stack proximate a flowchannel at the periphery of the fuel cell, the recess being adapted andconfigured to receive an end portion of a manifold mold. It is alsoenvisioned that the method can include positioning a manifold moldagainst the contoured portion.

The method can further include molding material around the fuel cell andmold to define the manifold. A first end plate of the fuel cell stackcan include a fill hole for receiving molding material and a second endplate of the fuel cell stack can include a vent hole to permit ventingof fluids and molding material to facilitate molding the plenum duringthe molding process. The method can also include the step of removingthe mold.

In accordance with a further aspect of the invention, the reductant flowfield can include a second reductant flow channel extending to aperiphery of the fuel cell and the oxidant flow field can include asecond oxidant flow channel extending to the periphery of the fuel celland the molding step can further include forming a second reductantmanifold in fluid communication with the second reductant flow channel,the second reductant manifold and the second reductant flow channelcooperating to form a second reductant plenum, and forming a secondoxidant manifold in fluid communication with the second oxidant flowchannel, the second oxidant manifold and the second oxidant flow channelcooperating to form a second oxidant plenum.

In accordance with still another aspect of the invention, the method canfurther include positioning a first end plate at a first end of the atleast one fuel cell and positioning a second end plate at a second endof the at least one fuel cell. The method can further include connectingthe first and second end plates to each other with a plurality offasteners to hold the fuel cell in place.

It is also contemplated that the method can include inserting at leastone removable runner mold into at least one of the oxidant flow channeland reductant flow channel to prevent molding compound from entering thechannel and to define a flow passage. The method can further includemolding material about the fuel cell and the runner mold to form theflow passage.

It is also envisioned that the method can further include removing therunner mold and inserting a manifold mold. The manifold mold can besubstantially cylindrically shaped. It is also contemplated that themanifold mold can taper along a direction from a first end of the moldto the second end of the mold. The method can also include moldingmaterial about the fuel cell and the manifold mold to form the manifold.It is also envisioned that the method can further include removing themanifold mold.

In accordance with a further aspect of the invention, the method canfurther include positioning a mold against the fuel cell, the removablemold having a shape that defines the volume of at least one of theoxidant manifold and reductant manifold. The mold can include anelongate manifold portion and a plurality of runner portions, the runnerportions being adapted and configured to contact flow passages in theperiphery of the fuel cell.

The method can further include molding material about the fuel cell andthe mold. It is also contemplated that the method can further includeplacing the fuel cell and mold inside of a mold cavity prior toperforming the mold operation, the mold cavity having a geometry fordefining a peripheral boundary of the fuel cell stack. The method canalso include removing the mold after removing the molding operation.

In accordance with another aspect of the invention, the method canfurther include integrally forming a tubular insert into the plenumhousing proximate an end of one of the manifolds, the tubular insertbeing made from a material that is compatible with the material of theplenum housing, wherein the tubular insert forms a portion of a fluidflow path including the manifold to which it is attached. The method canfurther include fitting an end plate of the fuel cell stack over thetubular insert such that the tubular insert protrudes through a port ofthe end plate of the fuel cell stack.

Material introduced during the molding step can be introduced by atechnique selected from among pressure assisted resin transfer, vacuumassisted resin transfer, injection molding, any other suitabletechnique, and combinations thereof. The material can be introducedunder a pressure differential of between about +15 psi and about −15psi. It is also envisioned that the material can be introduced bypressure assisted resin transfer under a positive pressure of between 0psi and about 250 psi. The material can be introduced by vacuum assistedresin transfer under a partial pressure of between about 750 Torr andabout 1 mTorr.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and are intended toprovide further explanation of the invention claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic of a typical electrochemical cellstack showing the various components.

FIG. 2 displays an exploded view of the stack components with runner andplenum inserts.

FIG. 3 is an example of a stack after the first molding step (two of sixplenum inserts are remaining in this illustration).

FIG. 4 shows an example of a 2-step, insert-molded stack after the finalmolding step.

FIG. 5 shows the stack components and the integral runner/plenum insertsin an exploded view.

FIG. 6 shows an assembly of the stack components, without the plenuminserts.

FIG. 7 shows an itemized assembly drawing of the stack with severalplenum inserts.

FIG. 8 shows the stack, as-molded, still in the mold with the plenuminserts still in place.

FIG. 9 shows the stack after de-molding with the plenum inserts still inplace.

FIG. 10 shows the voltage currant (V-I) curve for the stack shown inFIGS. 8 and 9.

FIG. 11 is a cutaway stack showing the integral plenums that are formedby removal of the inserts after the molding process.

FIG. 12 shows the use of discrete bridge components within a bipolarplate to provide the runner geometry required for single step molding.

FIG. 13 shows a stack which employs a vapor barrier component to reducecoolant permeation.

FIG. 14 shows a stack which incorporates a tapered manifold plenumgeometry.

FIG. 15 shows a stack design utilizing combination compressive(mechanical) and adhesive seals in relation to the junction of theterminal bipolar plates and the endplates.

FIG. 16 shows cell vapor leakage curves to demonstrate the effectivenessof vapor barriers in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

Before further description of the present invention, and in order thatthe invention may be more readily understood, certain terms are firstdefined and collected here for convenience.

As used herein, the term “plenum” means the geometry or component thatcreates the common volume of reactant and/or coolant manifolds, e.g.plenum 110 in FIG. 1.

The term “runners”, e.g. runners 128 in FIG. 1 are the sections of themanifold that distribute the reactant and/or coolant to the individualcells/flow fields (e.g. flow fields 1208 shown in FIG. 12 and fields1108 shown in FIG. 11). In certain embodiments, the runners areintegrated into the bipolar plates (e.g. integral runners 604 in bipolarplates 602 in FIG. 5) of the fuel cell stack (e.g. stack 100 in FIG.100). In another embodiment, the runners are molded in place with aninsert or inserts (e.g. runner inserts 202 in FIG. 2) that are removedafter molding. For both embodiments, the plenum is molded in place withan insert (e.g. insert 207 in FIG. 2) that is removed after molding.

The term “bridge” is a discrete component added to a flow field orbipolar plate to provide a runner without side drilling, e.g. bridge1202 in FIG. 12.

The term “manifold” is defined as the combination of the runners and theplenum, e.g. manifold 150 in FIG. 1.

MEA Stacks of the Invention

In certain aspects, the instant invention provides an electrochemicalcassette comprising, at least one electrochemical cell which comprises amembrane electrode assembly (MEA), a reductant flow field, an oxidantflow field, a separator plate, at least one reductant external manifoldand at least one oxidant external manifold, wherein each flow fieldcomprises at least one opening extending through the periphery of thecell and each external manifold comprises a primary manifold and atleast one port in fluid contact with the peripheral openings in the flowfield to which the external manifold is intended to deliver material,wherein the one or more MEA, oxidant flow field, reductant flow field,and separator plate, are assembled and encapsulated about the peripherythereof by a sealant; and wherein each external manifold is a volume atleast partially bounded by the sealant and wherein the volume is incontact with the peripheral openings in the flow field to which theexternal manifold is intended to deliver material.

In certain embodiments, the invention provides for an electrochemicalcassette, wherein each external manifold is a volume substantiallybounded by the sealant, e.g. molded region 170 in FIG. 1.

In another embodiment, the invention provides for an electrochemicalcassette, wherein each external manifold is a volume substantiallybounded by the sealant and at least one additional element comprising,the one or more MEA, oxidant flow field, reductant flow field, secondsealant layer, or separator plate. In a further embodiment, the externalmanifold is a volume substantially bounded by the sealant and themembrane electrode assembly or plate. In another further embodiment, theexternal manifold is a volume substantially bounded by the sealant and asecond sealant layer.

In yet another embodiment, the invention provides for an electrochemicalcassette, wherein each reductant external manifold and each oxidantexternal manifold comprises a volume substantially bounded by thesealant and optionally one additional fluid impermeable material,wherein the volume is defined by at least one removable mold elementwhich is fluidly connected with the peripheral openings of the flowfields to which the manifold is intended to deliver or remove material.In a further embodiment, the removable mold element is removed afterencapsulation of the periphery of the cassette with the sealant.

In other embodiments, the invention provides for an electrochemicalcassette, wherein a separator plate and one or two flow fields areintegrated into a bipolar plate and each flow field peripheral openingextends through only a portion of the thickness of the bipolar plate.

In a further embodiment, each flow field peripheral opening comprises anadapter capable of forming a fluid tight seal with the removable moldingelement placed in contact with the flow field peripheral openings. A“fluid tight seal” or “sealant tight seal,” which are usedinterchangeably herein is, e.g., a gas and/or liquid tight seal, whereinthe sealant may penetrate the edges of the MEA but is prevented fromentering the manifold opening. In another further embodiment, each flowfield opening extends through a portion of the surface of the bipolarplate and provides fluid contact between the external manifold and theflow field to which the manifold is delivering material. In anotherfurther embodiment, each flow field opening extends through a portion ofthe thickness of the bipolar plate without extending through the surfaceof the plate.

In a further embodiment, the adapter comprises a flat surface capable ofmating to a removable mold element having a planar surface or theadapter comprises a curved surface capable of mating to a cylindricalremovable mold element or an elliptical prism.

In another further embodiment, the removable mold element comprises amain body and a plurality of protrusions and the adapter comprises aconcave volume capable of forming a fluid tight seal with a protrusionof the removable mold element.

In still further embodiments, each flow field peripheral opening forms afluid tight seal to a molding element used to form the externalmanifold. In another further embodiment, the molding element is a solidbody comprising a plenum and at least one runner, wherein the plenumdefines the volume of the manifold and the runners form a fluid tightseal with each flow field peripheral openings such that the manifold isfluidly connected to the flow field after removal of the moldingelement. In another further embodiment, the cassette further comprisesat least one coolant flow field wherein each coolant flow fieldcomprises at least two opening extending through the periphery of theflow field and at least two coolant external manifolds each comprising aprimary manifold and at least one port capable of coupling to theperipheral openings in the coolant flow field. In still another furtherembodiment, each bipolar plate has zero or one oxidant flow field, haszero or one reductant flow field, and zero or one coolant flow field.

In other embodiments, the invention provides an electrochemicalcassette, wherein each membrane electrode assembly is in contact with areductant flow field and an oxidant flow field.

In another embodiment, the invention provides an electrochemicalcassette, wherein each reductant external manifold and each oxidantexternal manifold comprises a volume bound by a substantially homogenouscomposition, wherein each manifold comprises the primary manifold and atleast one port capable of mating to the peripheral opening of an equalnumber of flow fields to which the manifold is intended to deliver orremove material.

In a further embodiment, each external manifold is a volumesubstantially bounded by the sealant and at least one additional elementcomprising, the one or more MEA, oxidant flow field, reductant flowfield, second sealant layer, or separator plate. In further embodiments,the external manifold is a volume substantially bounded by the sealantand/or the membrane electrode assembly or plate. In a furtherembodiment, the external manifold is a volume substantially bounded bythe sealant and a second sealant layer.

In yet another further embodiment, each reductant external manifold andeach oxidant external manifold comprises a volume bound by the sealant.

In other embodiments, the invention provides an electrochemicalcassette, wherein the sealant contemporaneously seals the junctionbetween the removable molding element and the peripheral openings of theflow fields to which the manifold is intended to deliver a materialduring the encapsulation process wherein void formed by removal of themolding element forms the volume of the external manifolds fluidlyconnected to the flow fields to which the manifold is intended todeliver a material.

In still other embodiments, the invention provides an electrochemicalcassette, wherein each composite MEA and each separator plate comprisesno grooves, holes or other aperture extending through the entirethickness thereof.

In yet other embodiments, the invention provides an electrochemicalcassette, wherein cassette further comprises at least one coolant flowfield wherein each coolant flow field comprises at least two openingsextending through the periphery of the flow field and at least twocoolant external manifolds each comprising a primary manifold and atleast one port capable of coupling to the peripheral openings in thecoolant flow field.

In a further embodiment, each reductant external manifold and eachoxidant external manifold comprises a single component comprising theprimary manifold conduit and at least one port capable of mating withperipheral openings of an equal number of flow fields to which themanifold is intended to deliver material; and each coolant externalmanifold opening comprises a single component comprising the primarymanifold conduit and at least one port capable of mating to peripheralopenings of an equal number of coolant flow fields.

In still other embodiments, the invention provides an electrochemicalcassette, wherein each external manifold comprises at least two primarymanifolds and at least two sets of ports which are not fluidly connectedsuch that each primary manifold and each set of ports can deliver orremove material to flow fields to which each primary manifold isintended to deliver or remove material.

In certain embodiments, the electrochemical cassette is a fuel cellcassette.

In other embodiments, the bipolar plate is machined or molded out of atleast one of a carbon/polymer composite, graphite or metal.

In still other embodiments, the bipolar plate is stamped from a metalsheet. In a further embodiment, the bipolar plate is a graphite tape.The term “graphite tape” is graphite, formed, embossed, and infused withresin to harden into a shape; such as carbon polymer composite.

In other embodiments, the invention provides an electrochemicalcassette, wherein the sealant is introduced by pressure assisted resintransfer, by vacuum assisted resin transfer, or by injection molding. Ina further embodiment, the sealant or resin is introduced under apressure differential of between about +15 psi and about −15 psi. Inanother further embodiment, the sealant is introduced by pressureassisted resin transfer under a positive pressure of between 0 psi andabout 250 psi. In another further embodiment, the sealant or resin isintroduced by vacuum assisted resin transfer under a partial pressure ofbetween about 750 Torr and about 1 mTorr.

In other aspects, the invention provides an electrochemical cassetteprepared by the process comprising the steps of: (a) providing amembrane electrode assembly (MEA), a reductant flow field, an oxidantflow field, a separator plate, at least one removable molding element toform a reductant manifold, wherein each flow field comprises at leastone opening extending through the periphery of the cell and eachremovable manifold element has a three-dimensional volume which definesan external manifold comprising a primary manifold and at least one portcapable of coupling to the at least one peripheral openings in the flowfield to which the external manifold is intended to deliver material,(b) assembling the membrane electrode assembly (MEA), the reductant flowfield, the oxidant flow field, the separator plate, and the removablemolding element forming the reductant manifold, (c) sealing theperiphery of the cassette by applying a pressure differential to thecassette such that 1) the peripheral edges of the cassette areencapsulated together by a resin; and 2) the removal molding elementsforming the reductant manifold and the removable molding element formingthe oxidant manifold forms a reductant manifold and an oxidant manifold.

In one embodiment, the invention provides an electrochemical cassette,further comprising at least one removable molding element to form anoxidant manifold.

In another aspect, the invention provides an electrochemical cassetteprepared by the process comprising the steps of: (a) providing amembrane electrode assembly (MEA), a reductant flow field, an oxidantflow field, a separator plate, at least one removable molding element toform a reductant manifold, wherein each flow field comprises at leastone opening extending through the periphery of the cell and eachremovable manifold element has a three-dimensional volume which definesan external manifold comprising a primary manifold and at least one portcapable of coupling to the at least one peripheral openings in the flowfield to which the external manifold is intended to deliver material,(b) assembling the membrane electrode assembly (MEA), the reductant flowfield, the oxidant flow field, the separator plate, and the removablemolding element forming the reductant manifold, (c) sealing theperiphery of the cassette by applying a pressure differential to thecassette such that 1) the peripheral edges of the cassette areencapsulated together by a resin; and 2) the removal molding elementsforming the reductant manifold forms a reductant manifold; wherein theoxidant flow field is left open.

In certain embodiments, the invention provides the electrochemicalcassette, wherein each bipolar plate or separator plate is side drilledto include external manifold geometry as well as the typical flow fieldgeometry. In a further embodiment, each external manifold is bounded bythe sealant.

In certain aspects, the invention provides for a fuel cell stackcomprising: (a) at least one electrochemical cassette of the invention;(b) at least one end plate assembly; wherein the end plate is assembledon the top and/or bottom of the stack of one or more electrochemicalcassettes.

In one embodiment, the invention provides a fuel cell stack, wherein theend plate assembly is assembled with the electrochemical cassette(s)prior to encapsulation such that the end plate and fuel cellcassettes(s) are encapsulated and sealed in combination.

In another embodiment, the invention provides a fuel cell stack, whereina compression means is applied to the stack to provide compressive forceto the fuel cell stack. In certain embodiments, the compression occursbefore, during, or after encapsulation.

In other embodiments, the invention provides a fuel cell stack, whereinthe end plate assembly is attached to one or more electrochemicalcassettes after encapsulation of the electrochemical cassette(s).

In still other embodiments, the invention provides a fuel cell stack,wherein the end plate assembly is attached by a compressive seal.

In yet another embodiment, the invention provides a fuel cell stack,wherein at least one of the end plate assemblies is composed of athermoset polymer, a thermoplastic polymer, a metal, or a metal alloy.

In another embodiment, the invention provides a fuel cell stack, whereinat least one of the end plate assemblies is composed of a filled polymercomposite. In a further embodiment, the filled polymer composite is aglass fiber reinforced thermoplastic or a graphite reinforcedthermoplastic.

In another embodiment, the invention provides a fuel cell stack, whereinat least a portion of one of the end plates is composed of anelectrically conductive metal or metal alloy. In a further embodiment,at least a portion of the cassette or one of the end plate assemblies isa copper current collector.

In certain embodiments, the instant invention provides the advantage inthat the requirement for runner tubes is no longer necessary. Thegeometries of the manifold and runners are cast directly into thesealant. In a further embodiment, the geometries are formed by sidedrilling the bipolar plates to include the runner geometry within thebipolar plate, wherein the process is referred to as a one step moldingof the manifold. In a further embodiment, the runner hole geometry ismolded into the side of the bipolar plate. In another furtherembodiment, the bridge component within the bipolar plate is used toaccomplish the runner geometry without the side drilling of the bipolarplate, also referred to as a one step method. In other embodiments,separate runner and plenum molding pieces are used, herein referred toas a two step method. In other embodiments, the integral runner andplenum molding pieces are used.

In certain preferred embodiments of the invention, fuel cell stacks ofthe invention also comprise a vapor barrier (e.g. which reduces coolantpermeation. The permeation of coolant (in vapor form) through the stacksidewalls can lead to a significant coolant loss over time. Thisrequires periodic servicing of the fuel cell system to re-fill thecoolant reservoir. This effect is generally undesirable and one goal foroptimum fuel cell stack design is to reduce or eliminate thispermeation. To address this issue, the insert-molded fuel cell stack mayemploy a vapor barrier component. An example of this component, vaporbarrier 1350 shown in FIG. 13, is made to fit over the coolant, air, orfuel manifolds such that it substantially surrounds the manifold. Theskilled artisan will appreciate that the vapor barrier component may beconstructed from a variety of materials, preferably an impermeable orlow-permeability material (typically metal or plastic). The vaporbarrier may be assembled to the stack and then molded in place, oralternately, it may be applied to the stack after the molding and curingsteps. FIG. 16 shows results from permeation testing showingeffectiveness of the vapor barrier in 36-cell stack with 18 sq. cm (2.8sq. in.) per cell. In FIG. 16, water permeation was compared for cellstacks having no vapor barrier, having a vapor barrier, and having avapor barrier plus foil wrapped around the cell stack. As shown in FIG.16, the vapor barrier substantially reduces vapor loss from cell stacks,and the additional foil wrap further reduces vapor loss.

The unique design of the present invention also may include a taperedmanifold plenum geometry. This aspect of the invention includes taperedmanifold inserts 1440 such as those shown in FIG. 14. Preferably, theinserts are tapered on the side 1450 facing out from the stackcomponents, thereby facilitating a uniform mating feature for all of thebipolar and cooling plates. Used in accordance with the presentinvention, the tapered manifold inserts 1440 offer numerous advantages(e.g., more uniform velocity, pressure drop, and flow distribution) overconventional stack designs.

In yet other preferred embodiments, insert-molded stacks of theinvention utilize a combination of compressive (mechanical) and adhesiveseals. This sealing feature 1530, illustrated in FIG. 15, substantiallyreduces or eliminates cross-leaks and/or external leaks. In theconstruction of insert-molded stacks, the transition of the manifold atthe junction of the terminal bipolar plates and the endplates 1520 cancreate a leak path unless the molded compound has sufficient adhesion tothe endplates. The leak path can lead to cross-leaks and/or externalleaks.

To avoid the necessity of priming the endplates or otherwise preparingthem for adhesion to the molding compound, a combinationcompressive/adhesive sealing feature 1530 may be employed. This sealingfeature may be an o-ring or a short tube section that will adhere to themolded compound used in the stack construction. This creates an adhesiveseal that stops the leak path and contains it to its respectivemanifold. The o-ring or tube itself is compressively sealed to thetubular port (protruding through the bottom of the top endplate in FIG.15). The compressive seal prevents the leak path from progressing insidethe o-ring or tube. This combination of compressive and adhesive sealingcreates a convenient, tolerant, and reliable sealing arrangement.

In other embodiments, and with reference to FIG. 12, the presentinvention provides a manifestation of the insert molded method usingseparate runner/bridge components 1202. These components eliminate theneed for a hole in the bi-polar plates 602. The methods described abovebuild upon the sealing and molding steps, with improvements made in theintegration of the plenums to the plates. FIG. 12 shows how bridge 1202can cooperate with a terminal region of flow field 1208 to define a port1204 without the need for drilling bipolar plate 1201. Moreover, thecombination of bridge 1202 and the terminal region of flow field 1208make an integral runner feature 1206, eliminating the need for plenuminserts during molding, as further described below with respect to FIG.6. However, those of ordinary skill in the art will readily recognizethat a bridge could be used in conjunction with a bipolar plate to forma port without drilling, and also without forming an integral runnerfeature extending from the bipolar plate.

The single-step molding method utilizes bipolar plates 602 which alreadycontain the required runner geometry 604, as shown in FIGS. 6 and 7.Accordingly, only the plenum geometry needs to be created during themolding step. The plenums are created via vertically-inserted inserts606 which seal against the sides of the bipolar and cooling plates 602,and which are encapsulated during molding, shown prior to molding inFIG. 7, during/after molding in FIG. 8, and after de-molding in FIG. 9.

Referring now to FIG. 2, the two-step methods involve an initial moldingstep where the runner geometry is molded in place via runner inserts 202that fit inside the ports 204 in the bipolar and cooling plates 206 andextend outward from the stack components. During this step, the plenuminserts 207 are also molded in place; however the outside extent of theplenums remains open after this step due to the requirement that therunner inserts be removed horizontally out of the stack. It is alsopossible for the runners and plenums to be unitary as in integralplenum/runner inserts 506, shown in FIG. 5. After this initial moldingstep (see FIG. 3), a secondary operation (molding or adhering ofcomponents) is required to complete and enclose the plenum geometry, asshown in FIG. 4.

The current innovation allows for use of an external manifold with the‘one shot’ fabrication techniques previously described. In general, flowfields (e.g. 1108, 1208) are employed with a minimum edge beyond theactive area (e.g. 2-3 mm). The flow fields are open to the outside edgeto provide at least one input for the respective reactants. In flowfields utilized for the cathode side of a fuel cell at least one inputand one output are provided. Similarly, cooling flow fields can beemployed that have at least one input and one output opening on theoutside edges. Flow fields can be made from metal or carbon composites,or other materials compatible with the function of the fuel cell. Abipolar configuration of the flow field can also be utilized thatincludes two flow fields on either side of a single component. Membraneelectrode assemblies are cut to nominally the same size and dimensionsas the flow fields. The flow field and MEA components are layeredtogether specific to the stack design (including the number of cells,number and placement of the cooling layers, etc.). These components areroughly aligned such that the MEA active area is exposed to thenecessary flow fields (either within bipolar plates or as separatepieces) to form an assembly. This assembly can include any number ofcells and cooling layers consisting of the necessary flow fieldcomponents and MEAs relatively assembled. The resulting assembly can beheld together via a clamping force for the remainder of the process (forexample, by compression screw 710 shown in FIG. 7).

Typically the ports of the external manifolds and peripheral openings ofthe assembled stack of MEAs/bipolar plates or MEAs/flow fields/separatorplates are mated together to fluidly connect each manifold to the flowfields to which they are intended to deliver (or remove) material. Afterassembly, a sealant resin is introduced which contemporaneously sealsthe junction between the ports of the external manifolds and theperipheral openings of the flow fields to which the manifold is intendedto deliver a material and encapsulates the periphery of the assembledcassette.

In electrochemical cassettes of the invention which comprise a pluralityof MEAs or in which the electrochemical reaction generates a substantialamount of heat, it is generally desirable to incorporate one or morecoolant flow fields into the electrochemical cassette to dissipate heatgenerated during operation of the cassette. Although other arrangementsare suitable for certain applications, the coolant flow field istypically interposed in between sets of between about 1 and about 8 MEAlayers, or more preferably between sets of 2, 3, 4, 5, or 6 MEA layers.In electrochemical cassettes comprising at least one coolant flow field,each reductant external manifold and each oxidant external manifoldcomprises a primary manifold conduit and at least one port capable ofmating with peripheral openings of an equal number of flow fields towhich the manifold is intended to deliver material; and each coolantexternal manifold comprises a primary manifold conduit and at least oneport capable of mating to peripheral openings of an equal number ofcoolant flow fields.

Also contemplated by the instant invention is an electrochemicalcassette comprising, at least one electrochemical cell which comprises amembrane electrode assembly (MEA), a reductant flow field, an oxidantflow field, a separator plate, at least one reductant external manifoldand at least one oxidant external manifold, wherein each flow fieldcomprises at least one opening (e.g. 204, 1204) extending through theperiphery of the cell and each external manifold comprises a primarymanifold and at least one port in fluid contact with the peripheralopenings in the flow field to which the external manifold is intended todeliver material, wherein the one or more MEA, oxidant flow field,reductant flow field, and separator plate, are assembled andencapsulated about the periphery thereof by a sealant; wherein eachexternal manifold is a volume at least partially bounded by the sealantand wherein the volume is in contact with the peripheral openings in theflow field to which the external manifold is intended to delivermaterial; and wherein each external manifold comprises a primarymanifold (e.g. 1110 in FIG. 11) which consists of a single conduithaving a substantially uniform cross section along the length thereof.

The novel design of the externally manifolded electrochemical cassettesof the invention results in a larger percentage of the MEA surface areabeing utilized for the electrochemical reaction and smaller cassettes(e.g., overall cassette size and weight) for a given cassette capacity.The cassette design provided herein simplifies the manufacture andassembly of the components of the cassette. In accordance with theinvention, the active surface area of the cassettes is increasedsignificantly. In particular, the separator plates (or bipolar plates)and MEAs do not require any holes or other apertures extending throughthe thickness thereof as is the case with fuel cell assemblies utilizinginternal manifolding.

Cassettes of the invention include one or more plates comprising one ortwo reagent flow fields having at least one and preferably two openingsto each reagent flow field about the periphery of the plate. Morespecifically, the plates comprise at least one and preferably twoopenings per reagent flow field which are capable of forming a fluidtight seal with a port of an external manifold when the stack isencapsulated with a resin. Preferably, the peripheral openings of theflow fields or plates and the ports of the manifold are shaped such thatthey facilitate stack assembly and formation of a fluid tight seal whenpressure or vacuum is applied during resin encapsulation.

The following is a brief description of certain innovations described inUS20040247982A1, included here as reference: A. Cassettes of theinvention comprise a preformed external manifold which is manufacturedor assembled such that the ports of the manifold can mate withcorresponding peripheral openings in the assembled stacks of separatorplates, flow fields, and MEA to form the cassette. B. To the clampedassembly of fuel cell components, separate manifold pieces are added toconnect all the openings corresponding to a particular reactant input oroutput on each of the layers. These manifold pieces can be machined froma solid stock, cast from any number of materials, or molded from asuitable resin. C. In general, these manifold pieces need to fit snugglyto each of the stack components with which it interfaces. D. Theexternal manifold is assembled by providing a primary manifold tube,hose, or pipe, placing a series of openings through the side wall of theprimary manifold and inserting hosing, pipes or tubings for the ports inthe openings. Preferably the port tubing inserted into the manifoldopenings has substantially the same diameter such that the connectionbetween the ports and the primary manifold is fluid tight or is fluidtight after encapsulating the fuel cell with resin. Although anymaterial which is chemically stable to the sealant and the reactants,e.g., oxidant and/or fuel, are suitable for use in the preparation ofthe external manifold opening, preferred materials are non-conductingresins which have are sufficiently flexible to facilitate stackassembly. Typically preferred manifold materials are selected fromsilicone, Teflon, polyethylene, Tygon tubing, butyl rubber, and thelike. E. For use in fuel cell applications, cassettes of the inventionare typically utilized in the form of a stacked assembly comprising thefollowing components: membrane electrode assemblies (MEA), flow fields,separator plates and external manifolds. Preferably the stacked assemblyis then encapsulated in a resin to bind the MEA and separator plates andto seal the external manifolds to the separator plates or flow fieldsforming a conduit between the manifolds and at least some of the flowfields. In preferred embodiments, one or two flow fields and a separatorplates are provided in a single bipolar plate which is then stacked withMEA layers and other bipolar plates.

With respect to the description above, the present invention allows forsignificant improvements in manufacturability and performance. Due tothe elimination of the manifolds as separate components, parts count issignificantly reduced. The precision manufacturing steps in making themanifolds are eliminated. Small parts handling is significantly reducedby the elimination of the runner and plenum insertion and attachmentsteps. In addition, the resulting flow geometry from the plenums througheach runner is more consistent from cell to cell because the runnerfunction is accomplished with a drilling or molding step during thebipolar plate manufacture, as opposed to manual assembly of small tubecomponents.

The externally manifolded stack assembly is placed within a cavity moldand a resin is introduced around the components. The resin is driveninto the edges of the stack assembly either by pressure applied from theoutside of the stack, or by a vacuum applied to the stack internal (i.e.through each of the manifolds). Once hardened, either by cooling of athermoplastic resin or curing in the case of a thermoset resin, theencapsulated fuel cell stack can be removed from the mold. The resinserves both to seal the edge of each MEA, as well as to bind togetherall of the stack components, including the manifold pieces.

The final encapsulation can also include end plates (such as end plates120 shown in FIG. 1, end plates 620 shown in FIGS. 6 and 7, and endplates 1520 shown in FIG. 15) and current collector pieces allowing forfurther integration of the assembly process, as well as reliability ofthe end product. End plate components can include features to compressthe stack component parts, either before, during or after theencapsulation steps. Because the fuel cell is fabricated without theneed for separate gaskets, the compression required is only a fractionof that in a traditional fuel cell stack, and is used to maintain goodelectrical contact.

Fuel cells of the present invention provide several advantages overconventional devices which include, but are not limited to thefollowing: The majority of the component area is actively used in theassembly, i.e. only a small portion is used in the sealing/manifoldingof the stack, such that at least 80% or more preferably between 85% andabout 95% of the MEA cross-section is actively used for theelectrochemical reaction; continuously coated MEAs can be readily used(i.e. compatible with roll-to-roll processing of MEAs); encapsulation ofall the components within the stack provides robust product; componentpieces can be fabricated with very relaxed tolerances as sealing doesnot require gaskets and compression; reducing or preventing corrosion inthe stack by segregating the reactant streams from the end plates orcollector plates; reducing or preventing problems associated withexposure of the MEA to non-aqueous coolants by segregating the coolantstreams from the composite MEAs.

Preferably, all of the fuel cell components are cut to roughly the sameshape perimeter. In preferred embodiments the MEA layer is a solid sheetwithout cuts or other holes or channels through the thickness thereof,the bipolar plate(s) have one or two flow fields on opposing faces, andat least two apertures per flow field about the periphery of the bipolarplate which are open to each flow field. Preferably the apertures arecapable of coupling to a port in an external manifold to form a tightseal, thereby excluding the sealant.

Due to the porous nature of the gas diffusion layer (GDL) of the MEA,sealant introduced into the periphery of the MEA and bipolar plateinterpenetrates the GDL to seal the MEA and the bipolar plate togetherand seals the bipolar plate aperture to the port of the externalmanifold. In conventional processes, the polymer membrane is oftenrequired to extend past the GDL to provide a frame for sealing purposes.Consequently, this results in increased manufacturing costs. Incontrast, in accordance with the present invention, sealing is achievedwith a GDL and polymer membrane that are of substantially the same sizeand shape. This is advantageous as the MEAs used in the presentinvention may be fabricated on a continuous basis with the associatedreduction in manufacturing costs.

In certain applications, particularly where an increased amount or morehomogeneous distribution of material to flow fields is desired, theinvention contemplates electrochemical cassettes, in which, flow fieldsare in fluid contact with two or more external manifolds deliveringmaterial and two or more exhaust manifolds. The electrochemical cassettedesigns provided herein provide for multiple manifold-flow fieldconnections, in part because of the ease of cassette assembly and thelow cross-sectional area required for the flow field opening toindividual external manifolds. Thus, the cassettes of the invention mayin certain instances incorporate a plurality of material delivery and/orexhaust external manifolds which are in fluid contact with each flowfield of the stack.

Although exemplary assembly designs have been described, those skilledin the art will recognize that fuel cells can have any desired number ofcomponents assembled together depending upon the output requirements ofthe final fuel cell cassette. Regardless of the particular design, thecomponents are assembled to meet the requirements of the finished fuelcell. In each case, external manifolds having ports which are of a sizeand alignment suitable for coupling to each of the apertures toequivalent flow fields in each of the bipolar or separator plates/flowfields are then aligned with the stack assembly to form a seal with eachof the flow fields.

To seal the fuel cell cassette assembly described above using vacuumresin transfer molding techniques, the mold insert materials andgeometry are selected to allow for fluid communication to the reductant,oxidant and cooling geometry within the fuel cell cassette assembly.Then, a sealant is introduced around the perimeter of the assembledcomponents. A vacuum is pulled through each of the external manifoldswithin the assembly. The pressure differential pulls sealant into theedges of the assembly thereby sealing the periphery of the components inthe assembly together and forming the assembly into a finished fuel cellcassette. Sealant also permeates the GDLs of the MEAs. The perimetersealing is complete when the sealant binds the adjacent portions of theMEA.

To seal a fuel cell cassette using injection-molding techniques, sealantwould be injected around the periphery of the assembly including theexternal manifolding using a driving pressure means. The sealant is notintroduced into the interior conduits of the external manifolds or intothe flow fields which are open to the interior conduits of the externalmanifolds. In the preferred embodiment, a thermoplastic resin isutilized as the sealant around the edges of the assembly and allowed tocool and harden prior to removal of the fuel cell cassette from themold. A mold capable of accommodating the associated temperature andpressure is utilized. Alternatively, a thermoset resin can be used inthe same manner; curing with any suitable combination of time andtemperature.

The pressure differential and time required to accomplish the sealingprocess is a function of the materials used in the fuel cell cassetteconstruction. These include the viscosity and flow characteristics ofthe resin, and the type of gas diffusion layer used in the MEA. Thoseskilled in the art will be able to judge the appropriate time andpressure based on these parameters. Those practicing the invention mayalso ascertain the most appropriate time and pressure by visualinspection during the sealing process.

The resin or sealant used for encapsulation is selected such that it hasthe required chemical and mechanical properties for the conditions foundin an operating fuel cell system (oxidative stability, for example).Appropriate resins/sealants include both thermoplastics and thermosetelastomers. Preferred thermoplastics include thermoplastic olefinelastomers, thermoplastic polyurethanes, plastomers, polypropylene,polyethylene, polytetrafluoroethylene, fluorinated polypropylene andpolystyrene. Preferred thermoset elastomers include epoxy resins,urethanes, silicones, fluorosilicones, and vinyl esters.

In certain preferred embodiments, endplates (e.g. 120, 620, 1520) arebonded directly to the stacked assembly of MEA layers and bipolar platesduring the sealing steps described above. Alternatively, the end platescan be modified bipolar plates having a flow field on one surface andelectrical leads and/or various adapters on the other surface. Severalbenefits result from the use of this embodiment. Removing thecompression seal between the fuel cell cassette and conventional endplates improves the reliability of the fuel cell stack and substantiallydecreases the weight. Also, the incorporated end plates can include avariety of fittings to further simplify the fuel cell stack.

In a preferred embodiment of the invention, vacuum- or pressure-assistedresin transfer molding is used to draw or push the sealant (introducedfrom the external edge outside the stack) into the peripheral edges ofthe MEAs and around bipolar plates and manifolds. Preferably the sealantforms a non-porous composite with that portion of the GDL in contactwith the external edge of the MEA and with the bipolar plate such thatthe seal is liquid or gas tight. This embodiment of the invention ispreferred in that it offers ease in terms of manufacturing and istherefore a preferred sealing means for large volume manufacture of fuelcell cassettes.

Preferred composite membrane electrode assemblies suitable for use inthe fuel cell cassettes of the invention comprise a laminated membraneelectrode assembly including membrane, catalyst layers and gas diffusionlayers. Suppliers include 3M, DuPont, Johnson Matthey, W. L. Gore,Umicore, E-Tek, PEMEAS among others.

Preferred cassettes suitable for use in electrochemical and fuel cellapplications further include at least two current collectors which arepreferably integrated into the endplates. Thus, in preferred cassettes,at least a portion of one of the end plates is composed of anelectrically conductive metal or metal alloy. More preferably, at leasta portion of one of the end plates is a copper current collector. Themeans by which the end plates and fuel cell cassettes are assembled toform the fuel cell stack provided by the present invention is notparticularly limited and may include compression gasket seals, o-rings,or co-encapsulation in a resin and/or sealant. In preferred embodiments,the end plate is assembled with the fuel cell cassette prior toencapsulation by the resin and prior to introduction of the sealant suchthat the end plate and fuel cell cassette are encapsulated and sealed incombination, e.g., simultaneously.

In other preferred embodiments of the present invention, one or morefuel cell cassettes are manufactured, then aligned in a stack togetherwith one or more compression gaskets and end plates. Compression meanssuch as through bolts (e.g. 710 in FIG. 7), tie downs or othermechanical fasteners are attached to the fuel cell stack to mechanicallyseal the fuel cell cassettes and end plates.

In preferred embodiments, the external manifolds of individual cassettesare capable of forming liquid or gas tight seals with adjacent externalmanifolds of other cassettes.

The layer size and number of layers in the cassettes and stacks of theinvention are not particularly limited. Typically each flow field and/ormembrane assembly will be between about 1 cm² and about 1 m². However,as will be appreciated by the skilled artisan, larger and smaller flowfield layers and/or membrane assembly layers may be suitable in certainapplications. The layer size and number of layers the fuel cellcassettes and fuel cell cassettes of the invention are capable ofproducing a sufficient power supply for a variety of applications.Frequently, the power output of fuel cell cassettes and fuel cell stacksof the invention will range from about 0.1 W to about 100 kW, or morepreferably, from about 0.5 W to about 10 kW.

The fuel cells of the invention offer improved corrosion resistance andincreased operation lifetime due, in part, to spatial separation of thecollector/end plates from reagents manifolds. The external manifoldsdeliver the fuel and oxidant to the reagent flow fields through amanifold that is segregated from the collector plates and composite MEA.The corrosion of the current collectors, which are formed from aconductive metal or metal alloy, is prevented by isolating reagentscapable of oxidizing or otherwise reacting with the current collectorsto the external manifolds and the flow fields to which the manifoldsdeliver material. Similarly, separating the reagent manifolds from theMEA prevents exposing both surfaces of the MEA to the reagents flowingthrough the manifolds and thus prevents cross-cell potential problemsassociated with many conventional fuel cell designs. In addition,contact between the MEA and the coolant fluid is avoided.

Any conventional MEA is suitable for use in the fuel cell stacks of thepresent invention. Moreover, square, circular, rectangular or otherregular shaped MEA having nominally the same cross section as thereagent flow field plates or bipolar plates are suitable for use in thefuel cell stacks of the present invention. Composite MEAs are suitablefor use in the cells of the invention without additional modification,e.g., additional openings in the MEA structure or incorporation of anon-conductive gasket are not required. Incorporation of a substantiallyhomogenous composite MEA which has substantially the same cross-sectionas the flow fields and/or separator plates maximizes the portion of theMEA available for use in electrochemical reactions.

The improved fuel cell stack of the present invention can bemanufactured from conventional fuel cell components and can utilize bothinjection molding and vacuum assisted resin transfer molding, andpressure assisted resin transfer molding processes.

The present invention allows for the fabrication of fuel cell stackswith a minimum of labor, thereby dramatically reducing their cost andallowing for process automation. In addition, in the present inventionthe ports are sealed by adhesion of the sealant to the fuel cellcomponents, not by compression of the endplates or other means ofcompression. This reduces the compression required on the final stack,thus improving the reliability of the seals, improving electricalcontact and allowing for the use of a wider variety of resins. Further,end plates may be molded into the fuel cell cassette thereby producingan entire stack (e.g., fuel cell cassette and end plates) in one step.

Preferred fuel cell cassettes of the present invention are furtherillustrated by means of the following illustrative embodiment, which isgiven for purpose of illustration only and is not meant to limit theinvention to the particular components and amounts disclosed therein.

EXAMPLES

The present invention provides a variety of cassettes suitable for usein electrochemical applications and ion exchange applications. As notedabove, cassettes of the invention are particularly well suited for usein fuel cells.

Example 1 Two-Step Molding Methods

In general, the two-step methods involved an initial molding step wherethe runner geometry was molded in place via runner inserts that fitinside the ports in the bipolar and cooling plates and extend outwardfrom the stack components. During this step, the plenums were alsomolded in place; however the outside extent of the plenums remains openafter this step due to the requirement that the runner inserts beremoved horizontally out of the stack. After this initial molding step,a secondary operation (molding or adhering of components) was requiredto complete and enclose the plenum geometry.

Example 2 Separate Runner and Plenum Inserts

Removable inserts were used during the molding process to form both therunner and plenum geometry. The runner inserts were inserted into portsin the sides of the bipolar and cooling plates to seal out the sealantcompound from the interior regions of the stack. Separate individualinserts were used to form the runners, and the plenums were formed byseparate inserts that physically contact the runner inserts to form amolding seal.

For the first molding step, the plenum inserts were typicallyconstrained on the outside by the interior walls of the mold itself.After the initial molding, curing, and de-molding was complete, theplenum inserts were first removed from the exterior walls of the stack.This allows access to the runner inserts which may be individuallyremoved.

FIG. 2 displays an exploded view of the stack components with runner andplenum inserts. FIG. 3 is an example of a stack after the first moldingstep (two of six plenum inserts are remaining in this example).

Example 3 Discrete Runner/Bridge Components

In other embodiments, the plates do not have the runner geometry.Instead, the plates had a void to accept a runner/bridge component whichis a separate component. This component shuts off the silicone sealantfrom entering the runner and provides for the bridging function at theedge of the MEA. The advantage of this construction is that the platesdo not need to have any through hole features and do not need tighttolerances. The runner/bridges were made from thermoplastics,thermoplastic elastomers, thermoset elastomers or any other materialdesired. The runner/bridges had features to facilitate sealing to thebi-polar plates as well as the plenums. These runner/bridge componentscan accommodate larger tolerances than the integral bi-polar platerunner concept.

After the first molding step was completed and the inserts were removed,there were two basic techniques that may be employed to complete theplenum geometry. In the first technique, pre-formed components wereadhered to the surface of the stack to close off the exposed face of theplenums. These components may be as simple as flat sheets of plastic ormetal which cover the open sides of the plenums and are sealed aroundtheir perimeter. Alternately, the components may be partial tubes orother partially-closed shapes which are adhered to the surface of thestack.

In the second technique, a second molding step was used to create theremainder of the plenum geometry. Typically, a separate, larger mold wasused to allow for the molding compound to form the remaining side of theplenum around the plenum inserts. The plenum inserts were re-installedafter the removal of the runner inserts. The stack was then molded againto form the remainder of the plenum geometry.

FIG. 4 shows an example of a 2-step, insert-molded stack after the finalmolding step. In this figure, tubes 420 were molded in place at the topof the stack as a transition to connecting to standard tubingcomponents; however various interfaces or fittings may be molded inplace. After the molding step, the plenum inserts were simply removedvertically and replaced with the fittings seen in the complete stack.

Example 4 Integrated Runner/Plenum, Single-Component Inserts

In another aspect, the method was identical to the method of example 1,except that a set of inserts with both plenum and runner geometry wasemployed in the first molding step. These inserts were removedhorizontally from the sides of the stack. Using this technique, assemblyand de-molding steps are simplified through reduced small parts handlingand a lower parts count.

FIG. 5 shows the stack components and the integral runner/plenum inserts506 in an exploded view. As previously described, the runner insertswere inserted into the ports in the sides of the bipolar and coolingplates to seal out the molding compound from the interior regions of theplates.

After the first molding step was completed, the second step options wereidentical to the methods for the separate runner/plenum inserts. Insertswith only plenum geometry (no runners) must be employed if the plenumsare completed with a secondary molding step. Alternately, use theintegral runner/plenum inserts to mold a stack in a single step wasaccomplished if the inserts were made to be collapsible or flexibleenough to allow for the runner inserts to be removed through the moldedplenum geometry at the de-molding step.

Example 5 Single-Step Molding Using Bipolar Plates with Integral RunnerGeometry

The single-step molding method utilized bipolar plates which alreadycontained the required runner geometry. Accordingly, only the plenumgeometry needs to be created during the molding step. The plenums werecreated via vertically-inserted inserts which seal against the sides ofthe bipolar and cooling plates, and which were completely encapsulatedduring molding.

Example 6 Bipolar Plates with Integral Runners with Plenum Inserts

FIG. 6 shows an assembly of the stack components, without the plenuminserts. The holes forming the runner geometry in the sides of thebipolar and in the cooling plates are visible in this view.

FIG. 7 shows an itemized assembly drawing of the stack with the plenuminserts. Rod insert 701 provides the insert with stiffness throughoutits length so as to allow for the elastomer tube 606 to be sufficientlysupported to ensure a seal against each bipolar plate layer. Theelastomer tube serves to create the inside diameter of the molded plenumas well as to provide for some flexibility in sealing off eachindividual layer during the molding step. This flexibility allows fornormal production tolerances and slight misalignments of components. Topport 703 may be a silicone tube or other connection that serve as theprocess ports for the fuel cell stack. Top port 703 preferably canadhere to the molding compound of the stack to form a continuous plenumwithout mechanical or compressive seals. Reference numeral 620 refers tothe compression plates (or endplates) of the fuel cell stack. End plates620 have some geometry to allow for the aligning of the plenum insertssuch as plenum alignment feature 704, fill holes 706 and vent holes 708to facilitate the molding process.

The stack manufacturing process was somewhat flexible; a typical examplefollows:

1. Assemble all components of the stack (bottom endplate, bipolarplates, cut-to-size MEAs, current collectors (if used), top endplate,compression screws and hardware, sealing rings (e.g. sealing ring 709).Use various aligning fixtures as necessary to eliminate interferences.Insert compression screws and hardware; tighten slightly (hand tight).

2. Insert elastomer tubes over the rod inserts and then insert thetube/insert into the holes in the top endplate.

3. Insert the top ports over the inserts and down into the top endplate.

4. Tighten compression screws to specified value.

5. Assemble the mold and insert the stack

6. Inject the molding compound until the vent holes barely spill over

7. Cap the vent holes and apply the specified time/pressure to themolding compound

8. Remove molding equipment, plug the fill hole on the mold, plug thevent holes on the top endplate

9. Cure the stack in the mold for a specified time and temperature

10. Remove the stack from the mold, remove the plenum inserts

As an alternative, part of step 7 (capping the vent holes) can beeliminated if the vent openings in the mold are lined with anair-breathing, resin-blocking membrane. In this embodiment, the ventopenings act as vents until the injected resin completely coats themembrane surface lining the opening. Once the membrane is fully coated,it forms a pressure-tight seal for the remainder of the molding andcuring process.

Another alternative is to substitute vacuum-assisted transfer molding inplace of the pressure-assisted method in step 7. In this case, a vacuumis applied to the manifolds of the fuel cell stack at the completion ofthe mold filling. The vacuum is applied for a suitable time andmagnitude to create the sealing interfaces in the stack. When utilizingthis method, the mold inserts forming the plenums and/or runner geometrymust be in fluid communication with their respective flow fields withinthe stack. One method for accomplishing this is to utilize bipolarplates and separator plates with fully-integrated runner geometry(Example 6 above) and plenum inserts wrapped or sheathed in anair-breathing membrane. The membrane must not allow the molded resin topass through the membrane. The vacuum is then applied through the plenuminserts after the mold is filled completely and the membrane surface iscompletely coated in resin except where it is in fluid communicationwith the ports of the bipolar and separator plates of the fuel cellstack.

FIG. 8 shows the stack, as-molded, still in the mold. The plenum insertsare still in place. FIG. 9 shows the stack after de-molding. A similarstack to that shown in FIG. 9 was constructed and tested. This stack had4 cells and 2 cooling layers. The stack was found to be leak-free. TheV-I curve for this stack is shown below in FIG. 10. FIG. 11 is a cutawaystack showing the integral plenums that are formed by the inserts duringthe molding process. FIG. 12 shows a method of making the integralrunner, bipolar plates with a discrete bridge component allowing forbipolar plates with no undercuts. This design allows for theconstruction advantages of bipolar plates with integral runners andplenum inserts and simplified bipolar plate manufacture. The plates donot have the undercuts necessary to form the integral runners andtherefore can be made from a simplified molding, machining or stampingprocess without tight tolerances. The discrete bridge components couldbe made from any suitable material including thermoplastic elastomers.This variation of the integral runner bipolar plate construction hasvarious manufacturing and cost advantages.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the device and method of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention includemodifications and variations that are within the scope of the appendedclaims and their equivalents.

1. A method of manufacturing a fuel cell stack, comprising: a) providingat least one fuel cell including: i) a membrane electrode assembly; ii)a reductant flow field disposed proximate a first side of the membraneelectrode assembly, the reductant flow field including a reductant flowchannel extending to a periphery of the fuel cell; iii) an oxidant flowfield disposed proximate a first side of the membrane electrodeassembly, the oxidant flow field including an oxidant flow channelextending to the periphery of the fuel cell; b) molding a plenum housingabout the periphery of the fuel cell, the plenum housing at leastpartially defining: i) a reductant manifold in fluid communication withthe reductant flow channel, the reductant manifold and the reductantflow channel cooperating to form a reductant plenum; and ii) an oxidantmanifold in fluid communication with the oxidant flow channel, theoxidant manifold and the oxidant flow channel cooperating to form aoxidant plenum.
 2. The method of claim 1, wherein the fuel cell furtherincludes a coolant plate in thermal communication with the membraneelectrode assembly, the coolant plate including a coolant flow channelextending to the periphery of the fuel cell and the molding stepincludes forming a coolant manifold in fluid communication with thecoolant flow channel, the coolant manifold and the coolant flow channelcooperating to form a coolant plenum.
 3. The method of claim 2, whereinthe molding step defines an interior surface of at least one of the (i)oxidant manifold, (ii) reductant manifold and (iii) coolant manifold incooperation with a portion of the periphery of the fuel cell.
 4. Themethod of claim 3, wherein the portion of the periphery of the fuel cellincludes at least one of (i) an edge of the membrane electrode assemblyand (ii) an edge of a plate.
 5. The method of claim 1, furthercomprising integrally forming the reductant flow field and oxidant flowfield into a separator plate, the separator plate being chosen from thegroup consisting of (i) a bipolar plate and (ii) a cooling plate.
 6. Themethod of claim 1, wherein the reductant flow field includes a secondreductant flow channel extending to a periphery of the fuel cell and theoxidant flow field includes a second oxidant flow channel extending tothe periphery of the fuel cell and the molding step further includes: a)forming a second reductant manifold in fluid communication with thesecond reductant flow channel, the second reductant manifold and thesecond reductant flow channel cooperating to form a second reductantplenum; and b) forming a second oxidant manifold in fluid communicationwith the second oxidant flow channel, the second oxidant manifold andthe second oxidant flow channel cooperating to form a second oxidantplenum.
 7. The method of claim 2, wherein the coolant plate includes asecond coolant flow channel extending to the periphery of the fuel celland the molding step further includes: a) forming a second coolantmanifold in fluid communication with the second coolant flow channel,the second coolant manifold and the second coolant flow channelcooperating to form a second coolant plenum.
 8. The method of claim 1,further comprising positioning a first end plate at a first end of theat least one fuel cell and positioning a second end plate at a secondend of the at least one fuel cell.
 9. The method of claim 8, furthercomprising inserting at least one removable runner mold into at leastone of the oxidant flow channel and reductant flow channel to preventmolding compound from entering the channel and to define a flow passage.10. The method of claim 9, further comprising molding material about thefuel cell and the runner mold to form the flow passage.
 11. The methodof claim 1, further comprising positioning a mold against the fuel cell,the removable mold having a shape that defines the volume of at leastone of the oxidant manifold and reductant manifold.
 12. The method ofclaim 11, further comprising molding material about the fuel cell andthe mold.
 13. The method of claim 5, further comprising forming acontoured surface in the edge of each separator plate proximate a portof a flow channel at the periphery of the fuel cell, the contouredsurface being adapted and configured to mate with a removable manifoldmold.
 14. The method of claim 13, further comprising positioning amanifold mold against the contoured portion.
 15. The method of claim 14,further comprising molding material around the fuel cell and mold todefine the manifold.
 16. The method of claim 15, further comprisingremoving the mold.
 17. The method of claim 1, further comprisingintegrally forming a tubular insert into the plenum housing proximate anend of one of the manifolds, the tubular insert being made from amaterial that is compatible with the material of the plenum housing,wherein the tubular insert forms a portion of a fluid flow pathincluding the manifold to which it is attached.
 18. The method of claim17, further comprising fitting an end plate of the fuel cell stack overthe tubular insert such that the tubular insert protrudes through a portof the end plate of the fuel cell stack.
 19. The method of claim 1,wherein material introduced during the molding step is introduced by atechnique selected from the group consisting of: (ii) pressure assistedresin transfer, (ii) vacuum assisted resin transfer, (iii) injectionmolding, and combinations thereof.
 20. The method of claim 19, whereinthe material is introduced under a pressure differential of betweenabout +15 psi and about −15 psi.